Statistical climatologyA variety of
statistical methods that provide a basis for climate change research have been
developed and examined. In the analysis of trends in climate elements,
parametric (least-squares regression) and non-parametric (median of pairwise
slopes) methods have been compared. The two methods yield trend magnitudes that
differ only marginally even for non-normally distributed variables; the
difference between the trend estimates does not depend on the degree of
normality of the variable. Extreme value
analysis (employing the ‘annual maxima’ method with the Generalized Extreme
Value distribution, and a stochastic modelling with the first order
autoregressive model) was used to study extreme temperature events in climate
model outputs, and return period of severe heat waves (observed in 1994) and
record breaking summer one-day temperature (1983). Various parameter estimation
approaches were compared, with a special concern devoted to the maximum
likelihood and L-moment methods. Methods of non-linear time series analysis were applied to time series of rock
slope movements to study the rock slope dynamics. Nonequidistant records of
dilatometric measurements of relative displacements on rock cracks on stable
and unstable sandstone slopes (NW Bohemia – Hřensko) have been analysed and tested for possible nontrivial (e.g.
nonlinear and deterministic) dynamics. Simultaneously, time series of
meteorological parameters (temperature, precipitation, humidity) recorded at
the nearest stations were tested in search for their possible effects on
studied rock slope dynamics. In the statistical downscaling, which
consists in looking for statistical relationships between large-scale upper-air
variables with the local surface ones, research concentrates on the sensitivity
of climate change estimates to the selection of the downscaling model and
predictors. Stochastic weather generator
Met&Roll is being used for creating synthetic daily weather series
(precipitation, extreme temperatures, solar radiation) whose statistical
properties reproduce the observed series, and can be easily modified in order
to simulate weather under changed climatic conditions. The generator was
modified substantially; firstly, additional daily (e.g. wind, humidity) weather
variables could be generated by nearest neighbours resampling, secondly, the
synthetic weather series might follow up with the observed series at any day of
the year and fit the long-term weather forecast. The modifications were
inspired by needs of so-called PERUN system designed to provide seasonal
forecast of crop yields. The improved generator has been used widely in
assessments of climate change impacts. Five versions of the weather generator
were evaluated as to their ability to reproduce heat and cold waves and extreme
high and low one-day temperatures at more than 80 locations covering most of
Europe. Furthermore, we have examined the effects various methodological
options have on the detection of modes of variability by means of
principal component analysis. In particular, the choice of the similarity
matrix (correlation or covariance), type of grid (latitude-longitude or
equal-area), and rotation of principal components affect the resulting
patterns. Specifically, the North Atlantic Oscillation (NAO) should be
preferred to the Arctic Oscillation (AO) in describing the
leading mode of variability in the Northern Hemisphere.